Electrolytic recording



Patented Jan. 10, 1950 2,493,963 ELECTROLYTIC RECORDING Harold G. Greig, Princeton, N. J., assignor to Radio Corporation of America, a corporation of Delaware No Drawing. Original application October 14.

1944, Serial No. 558,717.

Divided and this application November 4, 1944, Serial No. 562,033

2 Claims.

The present invention relates to the electrolytic production of color images on a traveling web or band (which, for simplification, may be called a carrier) and particularly to the production of such images in facsimile recording while employing as a component for the production of the images a tetrazonium compound stabilized by means of an alkylolamine.

This application is a division of my copending application, Serial No. 558,717, filed October 14, 1944, entitled Electrolytic recording, now U. S. P. 2,459,521, dated January 18, 1949.

Solomon in U. S. P. 2,306,471 discloses the electrolytic production of color'images on a carrier by a number of methods, the most efficacious of which involves the electrolytic diazotization of a primary aromatic amine and the electrolytic coupling of the so-formed diazonium compound with a coupling compound. While very good records are obtained by this method, the records do not represent the optimum in these two very important aspects:

(1) Shade and depth ,of color of the images,

and

(2) Background permanence of the records to light.

The azo dyes which give the best recordsare dark blue, green and black dyes. While there are many components employed in the manufacture of azo dyestuffs which yield yellow, orange and red dyes, there are not so many components which give dyes simulating a black shade. The monoazo dyes which possess such shades are metal complexes of the dyestuff, usually with a metal such as chromium. The other dyes having such shade are trisazo dyes. The difficulties of introducing a metal into a preformed dye serving as an image record with the production of a modified record, are self-evident. Attempts to produce satisfactory records in this way met with little or no success.

It is of course possible to produce a record of a trisazo dye by starting with a receiver which is dyed with a monoazo dye and by effecting the formation of the trisazo dye under the printer bar. This, however, means that the receiver is originally dyed, making it diflicult and complex to handle the receiver prior to its use.

There are certain primary amines which upon diazotization and coupling yield deep blue dyes. Primary amines of this character are benzidine, dianisidine and the like. These compounds, however, are insoluble in water and hence cannot be used in the electrolytic diazotization and coupling method.

2 It has been found that with the electrolytic diazotization and coupling method, the impermanence of the background is attributable to three possible factors. The first of these involves the spontaneous formationof the dyestuff of which the record is composed. The coloring produced in this way, however, is dischargeable by alka-.

line sodium hydrosulfite solution. Another possibility involves oxidation of the coupler. The color thus produced also appears to be dischargeable. The third factor involves oxidation and polymerization and the color produced in this Way is not dischargeable.

It has been ascertained that coloring produced by the last of these methods is enhanced by primary aromatic amino groups, particularly when these are present in the coupling component. Attempts to modify these groups or to modify the structure of the'various couplers used in the electrolytic diazotization and coupling method so as to avoid this latter type of oolora tion have given some improvement but have not completely alleviated the condition.

It has now been discovered that the disadvantages inherent in the utilization of the electrolytic diazotization and coupling method can be. avoided by electrolytically producing the color' images while employing a tetra'zonium compound e. g. benzidine or dianisidine stabilized by means, of an alkylolamine.

It is accordingly an object of this invention to produce dyestuffs by reacting under the influence of an electrolytic current a coupling com-.- pound and tetrazotized benzidine or -dianisidinef stabilized with an alkylolamine.

It is a further object of this invention to electrolytically produce azo dyestufi records which are of a dark shade simulating black and which wherein A is an aryl radical and X is a radical of an aliphatic amine the amino nitrogen atom of which is linked to the azo group. When these compounds are subjected to the action of an electrolytic current, the compounds are split along the dotted line i ndicated in the formula.

The diazonium compound which has thus been regenerated is now capableof reacting with a coupling compound of the type usual in the formation of azo dyestuffs to give a dyestufi.

The diazoamino compounds falling within the above general classification and which are suitable for use in my process are those obtained by reacting alkylolamipe such as ethanolamine, 'iiiethanolamine or diisopropanolamin e with; tetrazotized benzidine or -dianisidine.

Examples of such diazoamino compounds are;

the following:

1 mol of tetrazotized dianisidine+2moles of diethanolamine 1 mol of tetrazotized benzidine+ 2,moles of diethanol amine.

These diazoamino compounds are employed 1 a nt ioi an. Ethylated beta naphthol, Amix r .f hr. io -0ni h l e-rain c acidarid diacetoacetyl f fhese various couplers, chromotropic. acid iahbbenfound to. g1ve'recordswhich excel from hi tand oint o ,ness qif ed n ack: round. perm nence and, he; h gnio p c acid" is "therefore pref rredf m qiind' ar pr ,"dianisidine and react-. l. alkylolarninestherewith n an alka ne g iit I ee o nd h t e. lativ fniop rtions fjthe amin act ng s a St bil fzcr retiree it 'q m i. o p u d is marked "significance In any case, itiis necessary to use an excess of the stabilizing; amineover iequanti hem tica ly:requi edtcjp uc e diazoamino compou "Preferably there should; if i edan m iits e; i i i/ii sam ne ingu to 0;5-per ce xcji ss 'oi theory, If the amountoj the stabili amineexcceds thejproportions given, the'sen ti vity'of the recording solution is: therebysubstantiallydepressed. It is therefore advisable to bear these ratios in mind in compounding the diazoaminojcompound.

' 'One-of the-particularadvantages in the utiliza-j tion of the above 'stabilizeidiazoamino compounds is thatitheyr may be, utilized in the form of water-insolublecompounds; Previously,stress has been placed upon the fact that compounds such as benzicline, dianisidine, and the like are primary aromatic amines which upon diazotization an coupling yield dyestuffs simulating shadesof black. 'Thiitil'i'zationef these-diazoamino "compounds, "therefore, permits the elec-- tr'olytic recording method to beexpanded to in-' include the utilization of those normally waterinsoluble primary aromatic amineswhich have been found 'to yield the fdarkest shades of dye-- s fs The" essential cemp'on'ents' for" the electrolytic" process are the stabilized diazoamino compound, the coupler, and an electrolyte in water solution or other dissociating solvent solution, such as alcohol. Ihe composition containing one or more of these essential ingredients is rendered alkaline so-as to have a pH ranging between 7.5 and 1 .5. The alkalinity can be effectedby the utilization of inorganic hydroxides, such as so- .dium hydroxide, potassium hydroxide, or the like.

Other ingredients may also be employed to facilitate. the operation. Thus penetration of the .receiver by the. recording composition is facilitated bythe use of. a wetting agent such as alkyl naphthalene. sulfonic acids, for example butyl naphthalene sulfonate and the like, the condensation productof a sulfonated benzene with The buffering agentv may be borax, sodium acetate, sodium carbonate or the like.

Where. a. question of stability, isinvolved this can often be resolvedby resort-ingto the use of reducing agents such ashydrazine, hydroxylamine and thelike. Whilethe reagentsenumerated: aboveare not-essential, they will in some instances. lead to an improved process. and'the formation ofimproved images, and their use in general is. recommended.

Thereceiver may-bepreparedfor the electro-. lytic-treatment in-various'ways. Thus, the re ceivermay be impregnated with anorganic-solvent-solution of the water-insoluble diazoamino compound, such as. an alcohol solution, and the. receiverisubjected to an' electric current in an electrolyte solution containing the coupler. Furthermore, a paste .may be made. ofthe. components, the paste applied to the receivenand the receiver subjectedto i electrolysis in an electrolyte solution. The invention contemplates the utilization of any method forbringing a receiver under the influence of an electrolytic current in the presence of a diazoamino compound, as above, an-electrolyte and a coupling compoundso as-t'o elfect-a springing of the diazonium compound from the-diazoamino compound and a couplingof the same with the coupling compound to -pro-- duce dye images in consonance-with the impulses imposed uponthe electrolytic cell. a

It is known in the'dyestuff art to utilize diazoamino compounds for the preparation of azodye-' stuffs. These compounds are-used in the dyestuff art in one oftwo methods. In the first method, fabrics and the like are uniformly dyedby impregnating the fabric with the diazoamino compound and regenerating the diazonium compound in the presence ofacoupli-ng compound. The second method involves printing a desi n on a fabric with a paste containing the diazoamino; compound anda coupling compound and regen-- eratingthe diazonium compound'by an afterdevelopment procedure. The diazonium compound is regenerated for coupling-in these'methods by resorting to the utilization of'steam, acid vapors, strong acids and the like.

'P'l'iere is, however, a, very marked distinction between'the'procedure adopted for use in the dyestuiT-art and the course ofthe reaction in mypresent electrolytic recording method. In

the dyestuif-art the whole fabric is permeatedf with the decomposing agent and should'this-be the fabric with a coupler and the decomposing.

agent the fabric will be uniformly dyed throughout.

In the electrolytic method, on the other hand, the color is developed only on one surface of the received. Thus if the receiver is a fabric when the electrolyzing current flows through the fabric between the electrodes, only a very small part of the receiver, 1. e., that which is in direct contact with the surface of the printer bar (anode) and which is backed by the helix (cathode) be-. comes acidic. The reverse side of the fabric becomes more alkaline. This condition, however, is only transitory for as soon as the current flow ceases the acidity is lost completely and alkalinity is automatically restored. The time of the current flow for any one particular spot is eceedingly small, being less than 10000 of a second for normal recordin speeds. The degree of acidity is variable being dependent on the current and the time of flow, and this mechanism thus permits a gradation in the amount of color formed, whereby the production of half tones is made possible. Such procedure is impossible in the dyestuff art since a gradation in the amount of color can only be effected in that method by limiting the amount of the diazoamino compound or coupler in the fabric and cannot be effected by control of acid development of the color.

There are other factors existing which also serve to distinguish the electrolytic method, on the one hand, from the prior art dyestuff method, on the other hand. The degree and permanence of acidity in the electrolytic method, as previously pointed out, is not comparable to the degree and permanence of acidity in the prior art method. Whether it is the acidity which prevails at the anode in the electrolytic method by which decomposition of the diazoamino compound results is not known and has not been ascertained. It is known, however, that during electrolysis a strong oxidizin action is present. This oxidizig action probably plays some part in the breaking of the diazoamino compound since the art recognizes the fact that many organic linkages are broken by the action of strong oxidizing agents.

Furthermore, during electrolysis nascent chlorine and oxygen are present so that in addition to the formation of the dye by coupling, side reactions undoubtedly ensue. These other reactions influence the course of the reaction, particularly with regard to the shade of the color formed. It is thus evident that the procedure herein contemplated cannot be considered even analogous to the prior art procedure of producing azo dyestuff from coupling compounds and stable diazoamino compounds.

Considerable attention has been paid above to the various types of coloring which produce background impermanence in electrolytic recording. It was stated that the coloring apparently attributable to oxidation and polymerization of the coupling compound is facilitated when there is present in the electrolyte a component having a primary aromatic amino group. Very surprisingly, however, the above diazoamino compounds which are per se stable to light, exert a stabilizing action to light upon the coupler precluding to a farreaching extent the aforesaid discoloration attributable tooxidation and polymerization. This, of course, means that after the electrolytic treatment the records obtained are much more permanent in their background on exposure to light than the records obtained by other electrolytic methods. An indication of the degree to which the above diazoamino compounds affect background stability may be seen from the fact that records made with the best solutions for the electrolytic diazotization type recording showed more discoloration when exposed to light for one day than records made according to the present method and exposed to light for one month.

These diazoamino compounds, therefore, have some very peculiar action on the coupling agents which leads to high light stability of the records, a fact which could never have been deduced from the nonanalogous employment of the diazoamino compounds in the dyestuif art in general.

The following examples will serve to illustrate my invention, although it is to be understood that the invention is not restricted thereto.

Example I 24.4 grams of dianisidine are slurried in 40 cc. of 38% hydrochloric acid and after being thoroughly wetted out, approximately 500 grams of water and 500 grams of ice are added thereto.

13.8 grams of sodium nitrite are dissolved in a small amount of water and the solution is run into the slurry at a temperature of 10 to 15 C. An excess of nitrous acid is maintained for half an hour and then is removed by the addition of a.

small amount of sulfamic acid. This procedure can he followed by spot tests on starch-iodide paper.

10 grams of activated charcoal are then added and the solution stirred for 15 minutes. The solution is then filtered.

The tetrazotized dianisidine thus obtained is then added slowly to a solution of 24 grams of diethanolamine and 36.8 grams of soda ash in 600 The diazoamino compound thus prepared insoluble in water. For sensitizing the receiver, a solution of the diazoamino compound is made in ethyl alcohol and the receiver treated therewith either by immersion or by spraying. A recording solution for use with the treated paper is then made up by dissolving .015 gram mol of chromotropic acid and 30 grams of salt, in a liter of water. Suflicient sodium hydroxide is added to the solution to give it an effective pH of 10.2. The solution is then used for wetting the paper, whereupon the paper is used in an electrolytic recording apparatus for the formation of dyestuff images thereon.

'Ihe. dyestuff images obtained aredarkc brilliant images on a yellow background; background: is highly resistant to color. changes;

Similar results. were. obtained when. utilizing; in; lieu-cot the chromotropicacid coupler; the: following; couplers:

p -Su1fophenylmethyl pyrazolone H-acid a Phenyl I acid Chloro'I-I acid l-naphthol-ifl-disulfonic acid Acetyl Hacid Beta naphth ol Naphthol RF" Ethylated beta naphthol and a mixture. of chromotropic acid-and-diaeetog acety-l. ethylene diaminel Example 1r 2.4 grams. of naphthol. A5 are. mixed with 1.28'grams..of. sodium hydroxide, (in the .form of.

a. concentrated. solution). and 2(1 cc...of boiling. water arepoured over the. mix:

' ture to give .a color-suspension. After cooling. a:.

to room temperature,

2 grams of a 40% solution of formaldehyde are added and the mixture diluted to a volume of 100 cc. 7 Recording paper is treated byimmersion in the above composition. The-paper isthen; coated.

with a paste made by mixing the dry diazoamino compound of Example I with sufiicient diethanolamine to give the desired consistency.

This paper is then passed through-a -'-i'ghtly alkaline solutiontof. salt and. water. and. subjected to the. action of an electrolytic currents There.- are formed onv the. paper, dyestuif images. which; are dark blue to purpl'ein color on a yellow background. The. records showaw high background stability to light.

It will be appreciated. thatinthisexample both the diazoamino compound and the coupler. are water-insoluble, but despite this .fact, very satisfactory records are neverthelessobtained;

Example III The procedure in this example isithe same as in Example Iiexcepting that the diazonium' compound which is stabilized is tetrazotized benzidine.

'- It is tobe understood that various modifica-f tions of my invention will bea pparent'to persons;-

sk'illed in: the art and 'I" thereforedo not'i ntend tobe limited in the patent granted except as a required by the'a'ppend'edclaims,

I claim:

1-. The process; of producing darlr colored-1 images on a relatively stabl'e background and on only one side of a fibrous traveling carrier by the electrolytic facsimile recording method: which:

carrier. which has been impregnated with an.

alkaline azc rdyefiorming composition comprising:

as its essential;components. a water soluble inorganic'sa-lt as the electrolyte inan amount. to

facilitate the passage; of the electrolytic recordlug current. a. diazoa-m-ino compound produced by reacting a. compound selected from the class}.

consisting of tetrazotized benzidine and tetraz otized. dianisidinei with. an :alkylolamine selected from. the-class consisting-of ethanolamine, di-

ethanolamine, and di-isopropanolamine, said diazoamino compound: being stable to light and air oxidation in an alkaline medium. and splitting under theinfl'uence ofythefleleetrolytic recording current to yield diazoni'um. ions, and a. suiii'cient quantity of. a coupling component to react withsai'dfldiazom'um ions when formed to produce an.

- 3 azo dye.

2: The; process. of producing dark colored images .ona relatively stable background. and; on: only one: side of afibrous traveling carrier by? theelectrolytic. facsimile i recording method which comprises impregnating the carrier: with an alcoholic solutionv of the: cliazoamino compound from tetrazotized' dianisi'dine and diethanolamine, said dia'zoamin'ol compound being split under the influence of: the. electrolytic re-.

cording. current toqyield diazonium ions, subsequently impregnating the carri'er'witl r an aqueous alkaline solution. containing-1 asrit's essential com.- ponent sodium chloride iman amount to facilitate the passage of. the electrolytic recordihgcurrent. and; chromotropib: acid aniaamount sumcient to: react with said diaz'onium ions when formedv to produce an azo dye, and subjecting the so treated. carrier to; the-"action ofiian electrolytic recording current...

' HAROLD: GREIG.

REFERENCES CITED The followingyreierences"are of record in the file of this patent:

'UNIIED STATES P TENTS- (Ir-HER. REFERENCES The Aromatic -Diazo--(Zom1 oounds and Their Technical Applications, by K. Saunders, 1936, 

1. THE PROCESS OF PRODUCING DARK COLORED IMAGES ON A RELATIVELY STABLE BACKGROUND AND ON ONLY ONE SIDE OF A FIBROUS TRAVELING CARRIER BY THE ELECTROLYTIC FACSIMILE RECORDING METHOD WHICH COMPRISES SUBJECTING TO THE ACTION OF AN ELECTROLYTIC RECORDING CURRENT SUCH A FIBROUS TRAVELING CARRIER WHICH HAS BEEN IMPREGNATED WITH AN ALKALINE AZO DYE FORMING COMPOSITION COMPRISING AS ITS ESSENTIAL COMPONENTS A WATER SOLUBLE INORGANIC SALT AS THE ELECTROLYTE IS AN AMOUNT TO FACILITATE THE PASSAGE OF THE ELECTROLYTIC RECORDING CURRENT, A DIAZOAMINO COMPOUND PRODUCED BY REACTING A COMPOUND SELECTED FROM THE CLASS CONSISTING OF TETRAZOTIZED BENZIDINE AND TETRAZOTIZED DIANISIDINE WITH AN ALKYLOLAMINE SELECTED FROM THE CLASS CONSISTING OF ETHANOLAMINE, DIETHANOLAMINE, AND DI-ISOPROPANOLAMINE, SAID DIAZOAMINO COMPOUND BEING STABLE TO LIGHT AND AIR OXIDATION IN AN ALKALINE MEDIUM AND SPLITTING UNDER THE INFLUENCE OF THE ELECTROLYTIC RECORDING CURRENT TO YIELD DIAZONIUM IONS, AND SUFFICIENT QUANTITY OF A COUPLING COMPONENT TO REACT WITH SAID DIAZONIUM IONS WHEN FORMED TO PRODUCE AN AZO DYE. 